According to the NIAID fact sheet on Botulism, the extreme toxicity of botulinum neurotoxins (BoNT) and the ease of production, transport, and delivery make this an agent of extreme bioterrorism concern. Nonetheless, although there are major vaccine development initiatives ongoing, there currently is no approved Botulinum toxin vaccine available. Advances in Botulinum research have designated the optimal target for vaccine development to be the non-toxic carboxyterminal half of the toxin heavy chain (HC50). In fact, an immediate research goal for NIAID is listed as the development of a HC50 fragment vaccine against botulinum neurotoxins. Therefore, this phase I research project proposes an innovative approach to the development of a botulinum toxin vaccine in that it will use recombinant technology to express the BoNT HC50 on the virion surface of rabies virus (RV) for use as a potential vaccine. The hypothesis, supported by multiple studies with RV, is that use of the killed RV containing the HC50 as a vaccine will greatly enhance the immune responses compared to using HC50 alone. RV has many attributes that make it an ideal candidate for a delivery vector for vaccine immunogens. This project proposes to 1) construct recombinant RVs expressing a chimeric RV G protein containing BoNT HC50, 2) characterize the immune response of mice immunized with the inactivated RV BoNT HC50 constructs to assess its extent and potency, and 3) challenge RV BoNT HC50-immunized mice with BoNT/A toxin to assess the level of vaccine protection.